Bug found in concat methods.

[Chris--A]

When printing using concat & concatln mixing certain methods can cause a compile error.

This occurred after moving the concat methods to their own module.

Example sketch which will no longer compile.

void setup() {
  Serial.begin(9600);
  Serial.println("Starting");

  byte rval = 255;
  byte gval = 100;
  byte bval = 232;  

  PrintEx serial = Serial;
  serial.concat(rval).concat(',').concat(gval).concat(',').concatln(bval);
}

void loop() {}